1. Field of the Invention
This invention relates to a golf club head and, more particularly, to a metallic hollow golf club head which is generally called as a metal wood.
2. Description of the Related Art
Recently, a large-sized metallic hollow golf club head has been proposed in order to attain a large moment of inertia and a low center of gravity. In a case of so called wood-type golf club head, it is said that an appropriate weight of the golf club head is approximately 200 g for an average golf player. Therefore, it is required to enlarge a golf club head within the aforementioned weight limitations.
A proposal on this kind of conventional golf club head has been made by Japanese Patent Laid-open Publication No. Hei 9-192273. In this golf club head, in order to enlarge the golf club head without changing the weight, the central area of the face including a sweet spot, is formed to have a thickness enduring the impact caused when hitting a ball, and the peripheral area around the central area is formed to have a thickness thinner than that of the central area. This enhances a spring performance of the face as a whole.
Another proposal has been made by Japanese Patent Laid-open Publication No. Hei 9-308713. According to this proposal, in order to provide a large-sized golf club head with a sufficient strength, a plurality of ridges are provided on a rear surface of the face vertically and/or horizontally.
In the meantime, enlarging the size of the golf club head and thinning the thickness of the face remarkably enhances the repulsion force, thereby enabling a longer carry due to so-called spring effects of the face. Therefore, many golf players prefer to use this kind of golf club.
On the other hand, there is a tendency that the player's score is greatly influenced by the selection of the golf club rather than the practice or technique of the player. Accordingly, the U.S.G.A. (United States Golf Association) is now trying to revise the golf rules so as to clearly regulate the spring effects of a golf club head.
In detail, the U.S.G.A is now trying to eliminate the unclear conventional definition on an "excess spring effect" by defining a concrete measuring method for measuring a repulsion coefficient of a spring effect, or a concrete devise for measuring the same.
In view of the above-mentioned trend, the metallic golf club head proposed by Japanese Patent Laid-open Publication No. Hei 9-192273 may become an improper golf club head in view of the revised golf rules because of the excessive spring effect.
On the other hand, the metallic golf club head proposed by Japanese Patent Laid-open Publication No. Hei 9-308713 may have a higher center of gravity because of the plurality of ridges formed on the whole area of the face. This contradicts the requirement for lowering the center of gravity of the golf club head.